The present invention relates to apparatus for forming flat surfaces on workpieces such as logs and cants of wood, and in particular to apparatus for simultaneously forming a sawn flat surface and chipping the material removed from the workpiece.
It is frequently desirable, because of the ease of disposal of chips as compared with irregular slabs of wood and bark, to cut the irregularly shaped waste material into chips when shaping a surface on a side of a log or edging a cant of wood. Log slabbing chippers are known in which a rotary chipper head has bent chipper knives having sharpened facing edge portions and sharpened chip cutting edge portions. In such a rotary chipper head the facing edge portions rotate in a plane which forms the finished surface of the workpiece, and the chipping edge portions of the chipper knives cut material removed from the workpiece into chips which may be used as pulp chips or raw material for pressed wood, chipboard and the like.
Maintenance of such chipper heads requires frequent sharpening of the chipper knives, and particularly the facing edge portions thereof, in order to consistently produce smooth flat surfaces. After sharpening, precise alignment of the facing edge portions of the chipper knives is required to provide a smooth flat surface. This alignment is time-consuming, yet it must be accomplished after each sharpening of the chipper knives.
Because a chipper takes bigger pieces of material from a workpiece than do the more numerous and smaller teeth of a saw, chipper knives are likely to break knots or crooked grained pieces from the surface of a workpiece rather than cut through them. Vibration of the last shaped end of the workpiece results in additional work which must be rejected because of surface irregularities. It has been found that because of these problems a smoother lumber finish may be produced if the workpiece surface is formed by first sawing the workpiece and thereafter chipping the scrap material. Apparatus for carrying out the operations of first sawing a flat surface and then chipping the scrap in one process has been disclosed in Chapman Canadian Pat. No. 940,016, and Mallery U.S. Pat. No. 3,880,215.
The Chapman patent discloses a chipper head having saw toothed segments mounted between the ends of the chipper knives such that the teeth of each segment extent radially beyond the edges of the chipper knives, at the end of the chipper head which contacts the workpiece. The ends of the chipper knives thus rotate within the kerf cut in the workpiece by the saw teeth.
While the Chapman apparatus provides a smoother surface than a chipper head alone, this manner of combining saw action and chipper head action is unnecessarily complex. Each saw toothed segment in the Chapman apparatus must be individually sharpened, set, and aligned in order to provide a smooth surface on the workpiece. The resulting gaps between the segments require the segments to be mounted eccentrically with respect to the axis of rotation of the chipper head in order to avoid uneven wear of the saw teeth. Separate segments also limit the distance by which the saw teeth can extend beyond the chipper head without very large gaps between teeth.
Mallery discloses a circular saw blade simply bolted to the end of a rotary chipper head, with the end of each chipper knife edge abutting against the saw blade. The saw blade is of greater diameter than the circular path or rotation of the abutting ends of the chipper knives, so that the saw blade cuts the workpiece ahead of the chipper. Since the chipper knives abut against the saw blade, however, the distance by which the radius of the saw blade can exceed the radius of the circle of rotation of the chipper knives is limited. With too great a saw blade radius slivers may wedge between the circular saw blade and the ends of the chipper knives, throwing the saw blade out of alignment. Such jamming of wood slivers may result in damage to the saw blade, and also produces unevenness of the surface of the workpiece. Any lateral movement between the saw blade and the chipper knives also results in noisy and potentially harmful hammering of the saw blade and chipper knives against one another.
What is needed, therefore, is an apparatus which does not require extensive or frequent maintenance and is capable of providing a smoothly sawn surface and chipping waste material in one operation. It is also desired to have such an apparatus which is simple to assemble and align and which is not adversely affected by slivers trimmed from a workpiece.